Formation permeability maintenance with hydroxy-aluminum solutions

ABSTRACT

The disclosure provides a method of treating a water-sensitive formation penetrated by a well by contacting the formation with a hydroxy-aluminum solution having a ratio of the hydroxyl groups to the aluminum atoms in the range of from 1.5 to 2.7.

United States Patent Inventor Marion G. Reed 3,013,607 12/1961 Bond eta1 166/292 X Hacienda Heights, Calif. 3,044,959 7/1962 Martin 25 2/8.55R Appl. No. 875,026 3,131,759 5/1964 Slusser et 211.. 166/305 R FiledNov. 10,1969 3,382,924 5/1968 Veley et 166/305 R Pntcnled Sepl.7, 19713,406,115 111/1968 White 252/855 R Amsiguet: Chevron Rewarcll Company mmu.; -u

Davis; 0, w., The Swelling of Bentonite And m (onlroL in ND & Eng. Chem,19(12), Dee. 1927, pp. 1350- 1352. FORMATION PERMEABILITY MAINTENANCE PYin 294)- WITH HYDROXY-ALUMINUM SOLUTIONS 5 Claims, 1 Drawing Fig.

Primary Examiner-Ian A. Calvert Attorneys-A. L. Snow, F. E. Johnston, R.L. Free1and,.1r. and

52 us. C1 166/305 R, B Keeling 166/292 [51] Int. Cl E211) 43/25 [50]Field of Search 166/275, 292-294, 305 R, 312; 252/855 R; 61/36 R;

210/42 ABSTRACT: The disclosure provides. a method of treating awater-sensitive formation penetrated by a well by contacting [56]Referencesc'ted the formation with a hydroxy-aluminum solution having 21UNITED STATES PATENTS ratio of the hydroxyl groups to the aluminum atomsin the 2,939,839 6/1960 flrnlgner 252/855 R range offrom 1.5 to 2.7.

ALUMINUM ALML' WATER on SALT ALKALINE BASE I 60 g 44 10 55 so 46 5B '452 A M MIXING PATENTED SEP H97! 3.603,, 399

ALUMINUM ALKALI SALT WATER ALKALfiq E BASE MIXING 34 TANK 4 INV E NT 0 RMAR/ON a. REED FORMATION PERMEABILI'IIY MAINTENANCE WITH ll'llYDIltOXY-ALUMINUM SOLUTIONS BACKGROUND OF THE INVENTION This inventionrelates to a method of treating a water-sensitive formation penetratedby a well and, more particularly, the invention provides for injectingdown a well and contacting with a water-sensitive formation ahydroxy-aluminum solution having a ratio of hydroxyl groups to aluminumatoms in the range offrom 1.5 to 2.7.

In petroleum producing operations, wells which penetrate oil-bearingformations are used to provide connection with the formation and thesurface. These wells may be producing wells through which oil isproduced, or injection wells into which water or other substances isinjected to promote oil recovery from adjacent wells which alsopenetrate the producing formation. In both types of wells the formationsadjacent to the wells are often contacted with foreign water duringproducing operations. Nearly all of these formations contain claymaterials of different types and in various amounts. The equilibrium ofthese clay materials is often drastically disturbed on contact withwater. Serious permeability losses can occur should the clay materialsobstruct flow by either expanding to fill pore spaces or by dispersingand lodging in pore constrictions. Oftentimes structural expansionoccurs when additional water is absorbed between clay layers. If largeamounts of expanding type or swelling clays are present, a verysignificant fraction of the flow channels may be closed by the increasedclay volume.

Clay particle migration is believed to be even a more serious damagemechanism than clay swelling. This is particularly true becausesubstantial amounts of damage can be done by this mechanism when thereis only a small amount of clay present in the formation. Clay particlesdispersed in the flow channels are carried downstream until they lodgein pore constrictions. Permeability of the formation is reduced by meansof these particles forming miniature filter cakes and filling these poreconstrictions.

A specific force acting on the expanding or swelling clays to expand thestructure is caused by the affinity of the exchangeable interlayercations and interlayer surfaces for water. Heretofore, organic cationssuch as amines have been used to decrease this tendency of the clays toexpand on contact with fresh water by replacing the exchangeable cationswith cations less inclined to attract water to interlayer sites.However, the organic cations have been not entirely satisfactory becausethey are expensive and they are also displaced from the clay surfacesafter time by reservoir brines.

Another force which causes both structural expansion of clays andparticle dispersion of clays results from the inherent negative chargeon almost all clay minerals. This charge is neutralized by absorption ofcations on clay surfaces. Since the cations tend to dissociate, apositive ion swarm is established in the solution near the surface ofthe particle and a negative charge exists within the particle. This isnormally referred to as an electric double layer. Particles with suchdouble layers repel each other and they tend to disperse. Since thestrength of repulsion is directly related to the dissociative tendencyof the absorbed cations, more firmly attached cations tend to decreasethe double layer thickness and thus to reduce the tendency of theparticles to disperse. This nullifies the inherent negative charge onthe clay surface. Heretofore, multivalent cations such as calcium havebeen used to treat water to sensitive formations. However, these cationsare readily exchangeable from clay surfaces by reservoir brines and thusgive only temporary protection under most conditions.

In summary, therefore, there is need for a method of treat ing suchwater-sensitive formations which provides positive and long lastingprotection for such formations from the adverse effects of theabove-discussed swelling and migrating clays.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides fortreating formations containing water-sensitive clays by contacting theformations with a hydroxy-aluminum solution having a ratio of thehydroxyl groups to aluminum atoms in the range of from 1.5 to 2.7. In atypical application, a water-sensitive formation penetrated by a well istreated with a solution formed by adding to water a quantity of aluminumsalts selected from the group consisting of aluminum chloride, aluminumbromide, aluminum iodide, aluminum nitrate, aluminum sulfate, andaluminum acetate, in an amount of between 0.01 and 24.0 pounds ofaluminum per barrel of water to form an aluminum salt solution and thenadding to such water an alkali or alkaline base in an amount of between0.95 and 1.7 pounds of hydroxyl ion for each pound of aluminum to form ahydroxy-aluminum solution. The aforesaid hydroxy-aluminum solution isinjected down the well and into the formation to stabilize thewater-sensitive clays in the formation. In many instances it isdesirable to follow the injection of the hydroxy-aluminum solution withan injection of fresh water. The well in some cases is shut-in to permitpolymerization of the hydroxy-aluminum solution in the formation tostabilize the water-sensitive clays in the formation.

OBJECTS OF THE INVENTION It is a particular object of the presentinvention to provide a method of stabilizing a formation containingwatersensitive clays by contacting the formation with a hydroxy-aluminumsolution. Further objects and advantages of the present invention willbecome apparent from reading the following detailed description in viewof the accompanying drawing which is made a part of this specification.

BRIEF DESCRIPTION OF THE DRAWING The drawing illustrates in schematicform an earth formation penetrated by a well which well has connectedthereto ap paratus for performing the method of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION The inventionfinds its utility in a well environment to stabilize clays in formationsof interest penetrated by the well. Referring specifically to thedrawing, a well 20 penetrating an earth formation 22 is shown. The well20 penetrates aproducing formation 24 which, for example, may containwater'sensitive clays which react when contacted by water to swell or tomigrate and to thus drastically reduce permeability of the for mation.Depending on the configuration of the well, it may be provided withsuitable packers 26 and 28 above and below the producing formation 24. Atubing string 30 provides fluid communication from the surface throughwellhead 32 to the producing formation 24. Suitable surface tubing 34connects the tubing string 30 with the discharge of a suitable pump 36.

A mixing tank 40 is connected to the intake of the pump 36 by a suitableconduit 42'. A valve 43 controls flow from the mixing tank 40 throughconduit 42 to the pump 36. The mixing tank 40 receives the materials forpreparing the hydroxyaluminum solution. In accordance with the presentinvention therefore means 4 defining a source of aluminum salt, means 46defining a source of water and means 48 defining a source of alkali oralkaline base are connected by suitable conduits to the mixing tank.Thus suitable tubing 50, 52 and 54 having adjustable valves 56, 58 and60, respectively, provides for the flow of the components from theirrespective sources to mix ing tank 4ltl for the formation therein of thehydroxy-aluminum solution.

It has been found that clay swelling and clay migration caused by watercontact in formations penetrated by a well can be substantiallyeliminated by contacting such formations with a hydroxy-alurninumsolution prepared in accordance with the present invention. Thehydroxy-aluminum solution should have a ratio of the hydroxyl groups tothe aluminum atoms in the range of from l.5 to 2.7. In a typicalapplication, the water-sensitive formation is treated with a solutionformed by mixing water first with a quantity of aluminum salts selectedfrom the group consisting of aluminum chloride, aluminum bromide,aluminum iodide, aluminum nitrate, aluminum sulfate and aluminumacetate. The selected salt is added in an amount of between 0.01 and24.0 pounds of aluminum per barrel of water to form an aluminumsolution. To this aluminum solution is added an alkali or an alkalinebase in an amount of between 0.95 and L7 pounds of hydroxyl ion for eachpound of aluminum to form a hydroxy-aluminum solution. The aforesaidhydroxy-aluminum solution is formed in the manner hereinafter describedin a suitable mixing tank and is then injected down the well and intothe formation to stabilize water-sensitive clays in the formation. Inmany instances, it is desirable to follow the injection of thehydroxy-aluminum solution with an injection of fresh water into the welland into the formation. The well is then shut-in to permitpolymerization of the hydroxy-aluminum solution in the formation tostabilize the water-sensitive clays contained in the formation.

The volume of the hydroxy-aluminum solution that should be injected intothe formation, of course, depends on the vertical interval of theformation and the distance out into the formation away from the wellthat it is desired to treat. Treatment volume depends on factors such asporosity, surface area and cation exchange capacity. Normally, onevolume of the preferred hydroxy-aluminum solution will protect onevolume of formation pore space. In certain formations, lesshydroxyaluminum solution will protect considerably more pore space. Forexample, in certain sandstones, one volume of the preferredhydroxy-aluminum solution will protect three volumes of pore space.Since the characteristics of formations vary, different treatmentvolumes will be required depending on the local formation conditions.Generally, however, it is preferred to inject one volume ofhydroxy-aluminum solution per volume of formation to be treated.

A particularly desirable method of treating a formation containingwater-sensitive clays includes forming a treatment solution by firstadding to water a quantity of an aluminum salt selected from the groupconsisting of chloride, bromide, iodide, nitrate, sulfate and acetate inan amount of between 0.0! and 24.0 pounds of aluminum per barrel. Thealuminum salt should be completely dissolved in water, after which analkali or alkaline earth base in an amount of about 0.95 and 1.07 poundsof OH for each pound of aluminum is added to the water. This material isslowly added to the solution while stirring vigorously. Addition of thebase should be made at the point of highest shear in the mixing system.The above materials are preferably added to the water at a rate so thatall the materials will be added in from 30 minutes to 1 hour. Theaddition of the alkali or AEB will cause precipitation in the system andthus clouding of the solution. However, after a period of time theprecipitate will dissolve and a clear solution will result. The time ittakes for the solution to clarify depends on the temperature, aluminumconcentration, stirring vigor and rate of addition of caustic. Thelatter two factors affect particle size of the precipitate and thus therate at which it dissolved. At about 75 F to 8 hours are required forthe solution to clear when prepared as above in the laboratory using aone-liter beaker and a magnetic stirrer. It is important that thesolution be clear prior to it being injected into the formation. Theclarified solution is injected down a well and into the formation. Afterthe injection of such solution, fresh water in an amount at least oneand not more that four times as much as the volume of thehydroxy-aluminum solution is injected into the formation. The well isshut-in for a time to permit polymerization of the solution in theformation to stabilize the clays therein. The well should be shut-in forapproximately 1 to 3 days.

A particularly preferred and highly efficient procedure for use in fieldoperations involves the use of aluminum chloride and sodium hydroxide inthe preparation of the hydroxy-aluminum solution. The solution isprepared by partially neutralizing an aluminum chloride solution withsodium hydroxide. The solution is prepared in the field by first fillinga large vessel with sufficient water to treat the desired volume offormation rock. As indicated above, this volume is preferably in a ratioof one volume of solution to one pore volume of the rock. The vessel isprovided with a means for vigorously stirring or circulating thesolution within the vessel. Aluminum chloride hexahydrate (A1Cl .6H 0)in an amount of 8.7 pounds per barrel of water is slowly added to thewater. After the aluminum chloride solution is prepared, sodiumhydroxide in an amount of 2.9 pounds per barrel is slowly added to thealuminum chloride solution. The sodium hydroxide is added to thesolution at the point which would provide the best mixing and at a ratesuch that all will be added in from 30 minutes to l hour. The mixturewill cloud during the addition of the sodium hydroxide due to theformation of a precipitate. However, the solution will clarify in timedepending on the temperature, the aluminum concentration, the stirringvigor, and the rate of addition of caustic. The clear hydroxy-aluminumsolution may be injected directly into producing and/or injection wellswithout pretreatment of the wells, except in the case of caustic wells.in this special case, the caustic must be purged from the well withbrine before injecting the solution to prevent undesirableprecipitation. The clear hydroxy-aluminum solution is injected into theformation and contacted with the water-sensitive clays found therein. Atthe termination of this injection, the formation is overflushed with lto 4 times, and preferably 3 times as much fresh water as thehydroxy-aluminum solution used. The well is then shutin for from one tothree days to allow for aging of the hydroxy-aluminum solution. Theshut-in period is not necessary in fresh water injection wells. Theshut-in period allows the hydroxyaluminum solution time to polymerize toa very stable and exchange-resistant material on silicate surfaces. Ifbrine flow is resumed too soon, aluminum may be displaced from the claysurfaces an incomplete conversion will result. After the aging, the wellmay be put back on production or injection.

Demonstrations have been conducted in the laboratory to illustrate theadvantages of the present invention. Variables used in the laboratorydemonstrations were concentration of the hydroxy-aluminum solution, theaging time of the formation after treatment and the aging medium in theformation during the aging time. Berea sandstone was used in thedemonstrations because after sodium saturation this sandstone is verysensitive to fresh water and this sandstone s composition and physicalproperties, particularly permeability, are quite uniform. In addition,it has been found that clay particle dispersion and migration are theprincipal damage mechanisms in Berea sandstone.

In the demonstrations, one inch diameter cores were cut from a largepiece of Berea sandstone. The cores were cleaned with toluene which wasthen evaporated in an oven at 70 C. The dry cores were vacuum-saturatedwith 0.3N CaCl and then flooded with deionized water in a Hassler cell.The permeability to water was then measured and used as the originalrock permeability. Some of the cores, as indicated below in Table I,were then flooded with ml. of 0.1M AlCl (OH/Al 0), others with 100 ml.of 0.1M Al(OH) Cl(OH/Al 2.0), and still others with 100 ml. of 0.1MAl(OH) Cl (OH/Al 2.4). Cores from each of these groupy were allowed toage for different periods of time, both with and without first washingout the excess aluminum salt. After the aging period, each core wasflooded with a liter of 0.1N NaCl and then with deionized water. Thiswas a severe test for water-sensitivity and also provided informationabout the exchangeability of aluminum and OH-Al ions on clay surfaces.Some of the cores were leached with additional NaCl (9 liters) todetermine whether longer exposure causes exchange of the aluminum and,in turn, greater permeability losses with deionized water. The data areshown in Table l.

TABLE I.-WATER SENSITIVITY OF BEREA SANDSTONE AFTER HYDROXY-ALL'MINUMTREATMENTS WITH DIFFERENT Oil/Al RATIOS, AGING PE RIODSAND AGING MEDIAPermeability to deionized water after XaCl floods (percent of Bycomparing water-sensitivities for different Ol-l/All ratios as shown inTable I, it is apparent that AlC ll alone (without prior conversion tohydroxyeluminum with a base) does not adequately provide lastingprotection for the rock against fresh water permeability damage.increased aging time was beneficial. However, even after 7 days, 87percent of the permeability was lost when the core was flooded withdeionized water after l liters of brine.

On the other hand, when the sandstone was treated with hydroxy'aluminumwith an Ol-l/Al ratio of either 2.0 or 2.4 and aged in fresh water therewas little, if any, fresh water-sensitivity even 10 liters of brine. itis also apparent that it is beneficial to age the rock in fresh waterrather than in the OH/Al solution. Therefore, after an OH/Al treatment,an overflush with fresh water is preferred. the data indicates, however,that the necessity for this overflush with fresh water is decreased iflonger shut-in periods or OH/Al solutions with a higher OH/Al ratio areused.

As indicated above, it has been found that wells containingwater-sensitive clays can be successfully treated by contacting theformation containing such clays with a hydroxy-aluminum solution havingthe formula AMOH ),,X;,,, where n has a value of between 1.5 and 2.7 andX is any anion selected from the group consisting of chloride, bromide,iodidefnitrate, sulfate and acetate. Particularly desirable results havebeen achieved when the ratio of the hydroxyl groups to the All atoms ismaintained in the solution within the range of from 2.0 to 2.4.

From the above description it is evident that the present inventionprovides a method of stabilizing water-sensitive clays found in aformation penetrated by a well by contacting the formation and thewater'sensitive clays contained therein with a hydroxy-aluminumsolution. Although only specific embodi ments of the present inventionhave been described in detail, the invention is not limited thereto butis meant to include all embodiments coming within the scope of theappended claims.

What is claimed is:

l. A method of stabilizing a formation penetrated by a well comprisinginjecting an aqueous hydroxy-aluminum solution down said well and intosaid formation, the ratio of the hydroxyl groups to Al atoms being inthe range of from 1.5 to

2. A method of stabilizing the permeability of a formation penetrated bya well comprising injecting down said well and into said formation asolution containing hydroxyaluminum having the empirical formulaAI(OH),,X where n has a value of between 1.5 and 2.7 and X is any anionin the group chloride, bromide, iodide, nitrate, sulfate and acetate.

3. A method of treating a water-sensitive formation penetrated by a wellcomprising adding to water a quantity of aluminum salts from the groupchloride, bromide, iodide, nitrate, sulfate and acetate in an amount ofbetween 0.411 and 24 pounds of Al per barrel, then adding to said wateralkali or alkaline earth base in an amount of between 0.95 and 1.7pounds of OH for each pound of Al, while vigorously stirring said waterto form a hydroxy-aluminum solution, clarifying said solution, injectingsaid clear solution down said well and into said formation, theninjecting fresh water in an amount at least i and not more than 4 timesas much as the volume of such hydroxy-aluminum solution :so injected,shutting said well to permit polymerization of said solution in saidformation and reopening said well for operation therein.

4. The method of claim 3 further characterized in that the aluminum saltis aluminum chloride and that the base is sodium hydroxide.

5. The method of claim 3 further characterized in that one volume ofsaid solution per volume of pore space of said formation is injectedinto said formation.

PO-YbbO UNITED STATES PATENT OFFICE Patent No.

Inventor(s) Dated September 7, 19 7 1 MARION G. REED It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Col. 3, line Col. line line line

Col. 5, line line line

Col. 6, line Signed and (SEAL Attos #3:

EDWARD I LFLETCHER ,JR. Attesting Officer "the-t should read than--.

"an" should read -and--;

"0.1M" should read --0.lM--;

"groupy" should read --groups-.

"the" should read The--;

II 1 u X n should read X II 3m should read X sealed this 30th day of May1972.

ROBERT GOTTSCHALK Commissioner of Patents

2. A method of stabilizing the permeability of a formation penetrated bya well comprising injecting down said well and into said formation asolution containing hydroxy-aluminum having the empirical formulaAl(OH)nX3 n where n has a value of between 1.5 and 2.7 and X is anyanion in the group chloride, bromide, iodide, nitrate, sulfate andacetate.
 3. A method of treating a water-sensitive formation penetratedby a well comprising adding to water a quantity of aluminum salts fromthe group chloride, bromide, iodide, nitrate, sulfate and acetate in anamount of between 0.01 and 24 pounds of Al per barrel, then adding tosaid water alkali or alkaline earth base in an amount of between 0.95and 1.7 pounds of OH for each pound of Al, while vigorously stirringsaid water to form a hydroxy-aluminum solution, clarifying saidsolution, injecting said clear solution down said well and into saidformation, then injecting fresh water in an amount at least 1 and notmore than 4 times as much as the volume of such hydroxy-aluminumsolution so injected, shutting said well to permit polymerization ofsaid solution in said formation and reopening said well for operationtherein.
 4. The method of claim 3 further characterized in that thealuminum salt is aluminum chloride and that the base is sodiumhydroxide.
 5. The method of claim 3 further characterized in that onevolume of said solution per volume of pore space of said formation isinjected into said formation.